This invention relates to a semiconductor device, more specifically to a semiconductor device with MOS field-effect transistors.
According to the conventional method, in forming a mask ROM, a plurality of source and drain regions are formed on a semiconductor substrate, gate insulating films or thick insulating films are selectively formed on the surfaces of portions of the semiconductor substrate forming channels between these source and drain regions, a plurality of input lines are respectively formed on these insulating films, and then an aluminium film for output line is formed with interposition of an insulating film composed of PSG (phospho silicate glass). When the output line aluminium film is connected with the drain regions of the MOS transistors formed on the semiconductor substrate, contact holes are respectively formed on these drain regions, and the output line is connected with the drain regions through these contact holes. According to such conventional mask ROM, the contact holes are required for connecting the output line with the MOS transistors, though the connection through the contact holes may often lead to disconnection of the output line, defective connection, etc., thereby reducing the yield rate. Furthermore, the contact holes will increase the chip area, preventing the reduction thereof.